The present disclosure relates to a spectrometer for generating a two dimensional spectrum.
A spectrometer is an instrument used to probe a property of light as a function of its portion of the electromagnetic spectrum, e.g. for spectrally resolving the light. The term ‘light’ or ‘radiation’ as used herein includes all forms of electromagnetic radiation such as visible, infrared and/or ultraviolet radiation. Typically, a spectrometer comprises reflective and/or refractive optics for guiding and shaping the light as well as a dispersion element such as a grating and/or prism for refracting, diffracting and/or dispersing the light in a wavelength dependent angle. Depending on the angle, different spectral components of the light can be imaged at different locations along a spectral axis in an imaging plane of the spectrometer. A sensor can be arranged for detecting spectral components of the light in the imaging plane.
In a typical spectrometer, light is dispersed along a single spectral axis. A disadvantage of such a spectrometer can be that for measuring a large bandwidth of light with a high resolution, a long (one dimensional) detector is needed to capture the spectral image. This can be alleviated by providing a spectrometer that generates a two dimensional spectrum, i.e. projects a two dimensional image wherein light is dispersed along two spectral axes. In this way the spectral image and corresponding detector can be more compact for a relatively high bandwidth and resolution.
EP1754032 B1 described a spectrometer assembly with a spectrometer for generating a radiation spectrum in a first wavelength range of a light source on a detector. The spectrometer comprises an Echelle grating for spectrally dispersing radiation entering the spectrometer assembly in a main dispersion direction. The spectrometer further comprises a dispersion element for separating the orders by means of spectrally dispersing the radiation in a lateral dispersion direction forming an angle with the main dispersion direction of the Echelle grating. The grating and dispersion element are adapted to generate a two dimensional spectrum with a plurality of separated orders. The spectrometer further comprises an imaging optical system for imaging the radiation entering through an entrance slit into the spectrometer assembly in an imaging plane. The spectrometer further comprises a detector array with a two-dimensional arrangement of a plurality of detector elements in the imaging plane.
U.S. Pat. No. 3,658,423 describes an Echelle spectrometer having an entrance aperture, at least one collimating mirror, a prism and an echelle grating which is so mounted to provide rotation in two directions thereby providing adjustment of the vertical and horizontal components of the dispersed energy in the exit focal plane. Optionally, the output energy from the spectrometer through a spectral focal plane passes through separate condensing optics to provide a first image of the grating face. Unfortunately, resolution is limited by optical aberrations.
U.S. Pat. No. 5,565,983 describes another Echelle spectrometer. The spectrometer includes a pair of crossed reflective gratings to effect a spectrally dispersed beam that is focussed to an array detector. The second grating is a plural grating with a surface formed of a first portion and a second portion. The plural grating surface preferably may be contoured to compensate for aberrations in focussing of the beam to the detector. The radiation is reflected from the grating into a further dispersed beam. These rays are thence passed to a concave spherical reflector which focuses the beam by way of an on-axis flat folding mirror and a field flattener lens onto a detector. Unfortunately, the folding mirror may be difficult to align and block a central path of the refracted beams.
There is yet a desire for an improved spectrometer for generating a two dimensional spectrum, in particular with regards to stability and manufacturability.